(1) Field of the Invention
The present invention relates generally to a method and apparatus for preparing liquid caustic solutions for use in fiber reactive dye baths, and more particularly to a method and apparatus for preparing liquid caustic solutions having a predetermined total and active alkalinities matching the reactivity requirements of a variety of fiber reactive dyes.
(2) Description of the Prior Art
Fiber reactive dyes are widely used in the dyeing of cotton and cotton blend fibers and fabrics. These dyes are easy to apply and produce brilliant shades, fastness, penetration and leveling. Exemplary fiber reactive dyes include trichloro pyrimidine, monochloro triazine, vinyl sulfone, dichloro quinoxaline, monofluoro triazine, difluoro-monochloro pyrimidine, dichloro triazine, and mixtures thereof.
Fiber reactive dyes are anionic in nature, and include a chromophore to give color to the dye and a reactive group which forms a strong covalent chemical bond between the dye molecule and the fiber, e.g., the hydroxyl group of a cellulose fiber. An alkaline dye bath is required in order to achieve the desired reaction or "fixing" between the dye molecule and the fiber. Various alkali compositions have been used in preparing fiber reactive dyes baths. These compositions include sodium hydroxide, potassium hydroxide, trisodium phosphate, sodium tripolyphosphate, sodium carbonate, sodium bicarbonate and sodium silicate.
Another composition, described in U.S. Pat. No. 4,555,378 to Moran, is a liquid phosphate system sold under the trademark Alkaflo by Sybron Chemicals of Birmingham, N.J. Another commercial liquid alkali or caustic is sold under the trade name Burco NP-Q Salt by Burlington Chemical Co., Burlington, N.C. This latter product is based on a mixture of sodium hydroxide, potassium hydroxide, soda ash, citrate and acrylate salt.
Also, U.S. Pat. No. 5,382,262 to Moore (hereinafter the '262 patent), assigned to the assignee of the present invention and incorporated herein by reference in its entirety, describes a buffered liquid alkali composition for use in fiber reactive dyeing formed by the "in situ" reaction of carbon dioxide with liquid potassium hydroxide i.e., liquid caustic potash, until the pH value of a 2% solution is about 12, resulting in an aqueous buffered alkali comprised of a super saturated mixture of potassium carbonate and potassium hydroxide. Potassium citrate and potassium polyacrylate may be included as dispersants and crystallization inhibitors.
Fiber reactive dyes are characterized by different rates of reactivity, requiring the use of a dye bath having sufficient total alkalinity to achieve the desired reaction between the dye and the fiber, but insufficient alkalinity to cause hydrolysis of the dye with the water in the dye bath, forming a nonreactive pigment. Thus, the user must select an alkali composition that will have a high enough total alkalinity to achieve the desired reaction, but sufficient buffering to avoid hydrolysis.
Fiber reactive dyes normally include instructions to guide the user in alkali selection. These instructions include recommended alkali baths for use in dyeing of fibers with the particular fiber reactive dye. The user can then prepare an alkali bath using the alkali composition recommended, and often sold, by the dye manufacturer. While optimum dyeing conditions can normally be achieved in this manner, practical and economic difficulties arise when the user is involved in dyeing different materials using different dyes. Under these circumstances, which commonly arise within dyeing facilities, it is necessary for the user to store separate alkali compositions for each dye to be used, and to maintain a separate supply source for each alkali composition needed.
Thus, there remains a need for a new and improved method and apparatus for eliminating the necessity for stockpiling of separate alkali compositions for each dye used while, at the same time, eliminating the need for a separate supply source for each alkali bath thereby resulting in a considerable improvement in operating costs and convenience.